This invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to developer and toner compositions containing charge enhancing additives, which impart or assist in imparting a negative charge to the toner particles and enable toners with rapid triboelectric charging characteristics. In embodiments, there are provided in accordance with the present invention negatively charged toner compositions comprised of toner resins, pigment particles or dye molecules, and certain metal charge enhancing additives. In another embodiment, the present invention is directed to toners with metal charge enhancing additives, which additives can be obtained, for example, from the reaction of a metal ion, such as aluminum or zinc ion with an ortho-hydroxyphenol, and an aromatic carboxylic acid in the presence of an appropriate base such as potassium hydroxide. The aforementioned charge additives in embodiments of the present invention enable, for example, toners with rapid triboelectric charging characteristics, extended developer life, stable triboelectrical properties irrespective of changes in environmental conditions, and high image print quality with substantially no background deposits. Also, the aforementioned toner compositions usually contain a colorant component comprised of, for example, color pigments or dyes, such as black, cyan, magenta, yellow, blue, green, red, or brown color, or mixtures thereof, thereby providing for the development and generation of black and/or colored images. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic, imaging and printing processes, including color and digital processes.
Toners with negative charge enhancing additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of toner resins, pigment particles, and as a charge enhancing additive ortho-halophenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives. In U.S. Pat. No. 4,845,003, there are illustrated negatively charged toners with certain aluminum salt charge additives. More specifically, this patent discloses as charge additives aluminum complexes comprising of two or three hydroxybenzoic acid ligands bonded to a central aluminum ion. While these charge additives may have the capability of imparting negative triboelectric charge to toner particles, they are generally not efficient in promoting the rate of triboelectric charging of toner particles. A fast rate of triboelectric charging is particularly crucial for high speed xerographic machines since, for example, these machines consume toner rapidly, and fresh toner has to be constantly added. The added uncharged toners, therefore, must charge up to their equilibrium triboelectric charge level rapidly to ensure no interruption in the xerographic imaging or printing operation. Another shortcoming of these charge additives is their thermal instability, that is they often break down during the thermal extrusion process of the toner manufacturing cycle. Most or many of these and other disadvantages are eliminated, or substantially eliminated with the metal complex charge additives of the present invention.
Toner compositions with other negative charge enhancing additives include, for example, those described in U.S. Pat. Nos. 5,300,387 and 5,302,481, the disclosures of which are totally incorporated herein by reference. Specifically, the '387 patent discloses toner compositions comprised of a toner resin, a colorant, optional surface additives and a metal complex charge additive derived from the reaction of a dicarboxylic acid and a hydroxybenzoic acid with a metal ion. Structurally, these charge enhancing additives are anionic metal complexes containing an anion comprised of a central metal ion, such as aluminum, gallium, zinc, cobalt ion and the like, bonded to two different bidentate ligands derived from an aromatic dicarboxylic acid and a hydroxybenzoic acid, and a countercation of proton, ammonium ion, alkaline metal cation or the like. Similarly, the '481 patent describes toner compositions with aluminum charge additives with mixed ligands derived from hydroxyphenol and hydroxybenzoic acid. While these charge additives are effective in imparting negative charge to toners, their rates of charging are generally in many instances not as rapid as those of the additives of the present invention, and their preparative processes are not as simple as the preparation of the charge additives of the present invention. Another advantage of the charge additives of the present invention is that they can be obtained from economical precursors. There are also disclosed in U.S. Pat. No. 5,409,794, the disclosure of which is totally incorporated herein by reference, toner compositions containing negative charge additives derived from the reaction of a metal, a metal carbonyl, a metal salt, or a metal oxide with a .beta.-diketone, a .beta.-keto ester, or a malonic ester in an aqueous or organic medium. These charge additives render toner compositions negative in triboelectric charging, but their charging rates are generally slower than those of the charge additives of the present invention.
Developer compositions with charge enhancing additives, which impart a positive charge to the toner particles, are also well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions; U.S. Pat. No. 4,221,856 which discloses electrophotographic toners containing resin compatible quaternary ammonium compounds; U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, illustrates developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition; and U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, illustrates positively charged toner compositions with resins and pigment particles, and as charge enhancing additives alkyl pyridinium compounds.
Illustrated in U.S. Pat. No. 5,391,453 is a negatively charged toner composition comprised of resin, pigment or dye particles, optional surface additives, and an aluminum complex composite charge additive containing active charge enhancing components as represented by the following formulas ##STR1## wherein R is a hydrogen, halogen, alkyl, aryl, alkoxy, aryloxy, hydroxy, nitro, or an amino substituent; Ar represent an aromatic group; M + is a proton, an alkaline metal cation, or an ammonium ion; and m is a number of from 1 to about 3; and in U.S. Pat. No. 5,332,636 there is illustrated a negatively charged toner composition comprised of resin or resins, pigment particles, optional surface additives, and an aluminum charge enhancing additive represented by the following formula ##STR2## wherein R and R' are independently selected from the group consisting of hydrogen, alkyl, aryl, alkoxy, aryloxy, hydroxy, halogen, amino, cyano, and nitro; R" is hydrogen or hydroxy; M + is a countercation comprised of a proton, an ammonium ion, a substituted ammonium ion or a metal cation; and x and y are the numbers 1 or 2, the disclosures of which are totally incorporated herein by reference.
In U.S. Pat. No. 5,256,515 is a negatively charged toner composition comprised of resin particles, pigment particles, optional surface additives, and a halogenated salicylic acid complex charge enhancing additive of the following formula ##STR3## wherein Z is zinc or chromium; M is hydrogen, an alkali metal, an alkaline earth metal, NH.sub.4, or NR.sub.4 wherein R is alkyl; X and Y are independently selected from the group consisting of chloride, iodide and bromide; and n and m are the numbers 1 or 2; in U.S. Pat. No. 5,256,5 is a negatively charged toner composition comprised of resin particles, pigment particles, optional surface additives, and a halogenated salicylic acid charge enhancing additive of the following formula ##STR4## wherein X is halogen, M is hydrogen, an alkaline earth, an alkali metal, or NR.sub.4 wherein R is alkyl, and n is the number 1 or 2; and in U.S. Pat. No. 5,300,389 is a negatively charged toner composition comprised of resin particles, pigment particles, optional surface additives, and a halogenated aluminum salicylic acid complex charge enhancing additive of the following formulas ##STR5## wherein M is hydrogen, an alkali metal, an alkaline earth metal, NH.sub.4, or NR.sub.4 wherein R is alkyl; X and Y are independently selected from the group consisting of iodide, chloride and bromide, and n and m are the numbers 1 or 2, the disclosures of which are totally incorporated herein by reference.
Although many charge enhancing additives are known, there continues to be a need for charge enhancing additives which provide toners with many of the advantages illustrated herein. There is also a need for negative charge enhancing additives which are useful for incorporation into black and colored toner compositions which can be utilized for developing positive electrostatic latent images. Moreover, there is a need for colored toner compositions containing charge enhancing additives which do not interfere with the color quality of the colorants present in the toners. Another need relates to the provision of toner compositions with certain charge enhancing additives, which toners in embodiments thereof possess substantially stable triboelectric charge levels, and display acceptable rates of triboelectric charging characteristics. Furthermore, there is also a need for toner compositions with certain charge enhancing additives based on aluminum complexes with both salicylate and catechol ligands, which possess excellent dispersibility characteristics in toner resins, and can, therefore, form stable dispersions in the toner compositions. There is also a need for negatively charged black and colored toner compositions that are useful for incorporation into various imaging processes, inclusive of color xerography, as illustrated in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference; laser printers; and additionally a need for toner compositions useful in imaging apparatuses having incorporated therein layered photoresponsive imaging members, such as the members illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Also, there is a need for negative toner compositions which have desirable triboelectric charge levels of, for example, from between about -10 to about -40 microcoulombs per gram, and triboelectric charging rates of less than about 120 seconds, and preferably less than 60 seconds, for example from about 15 to about 30 seconds, as measured by standard charge spectrograph methods when the toners are frictionally charged against suitable carrier particles via roll milling. There is also a need for nontoxic, substantially nontoxic, or environmentally compatible charge enhancing additives, which when incorporated at effective concentrations of, for example, less than 7 weight percent, preferably less than 5 weight percent in toners, render the toners to be environmentally friendly. An additional need resides in the provision of simple and cost-effective preparative processes for the aluminum complex charge enhancing additives of the present invention. The concentrations of the charge additives that can be incorporated into the toner compositions generally range from about 0.05 weight percent to about 5 weight percent, depending on whether the charge additive is utilized as a surface additive or as a dispersion in the bulk of the toner. The effective concentrations of toner in the developer, that is toner and carrier particles, are, for example, from about 0.5 to about 5 weight percent, preferably from about 1 to about 3 weight percent.
Illustrated in U.S. Pat. No. 5,438,829 is a negatively charged toner composition comprised of a polymer resin or polymer resins, colorants comprised of pigment particles and/or dyes, optional surface additives, and a boron charge enhancing additive obtained from the reaction of an alkylboric acid or an arylboric acid and an N-alkyl-or N-aryl-substituted bis(hydroxyalkyl)amine, or a zinc charge enhancing additive obtained from the reaction of an aromatic carboxylic acid and an N-alkyl- or N-aryl-substituted bis(hydroxyalkyl)amine with a zinc ion-containing compound in aqueous medium; and U.S. Pat. No. 5,532,098 is a toner composition comprised of toner resins, colorants, optional surface additives, and a charge enhancing additive obtained from the reaction of an aluminum ion-containing compound with a molar equivalent of an aromatic carboxylic acid, and an excess of an N-alkyl or N-aryl-substituted bis(hydroxyalkyl)amine in an aqueous medium at a temperature ranging from about 25.degree. C. to about 100.degree. C., the disclosures of which are totally incorporated herein by reference.